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Common FAQ: Questions common to all platforms

See also top-level FAQ page.

List of questions in this category

Who deletes all the windows I create?

All windows and controls in wxWidgets programs are created using new but you shouldn't use delete to free them. This doesn't result in memory leaks because wxWidgets takes care of this: all objects derived from wxWindow will be deleted automatically by the library when the corresponding real, on screen, window is destroyed. Thus, the top level window objects are deleted when you call Close() or Destroy() and all the child windows are deleted just before the parent window is. More details about the top level windows can be found in the ``Window deletion overview'' in the manual.

wxWidgets also automatically deletes some other kind of the objects, notably the sizer or constraint associated with the window -- this happens just before the window itself is deleted. The sizers, in turn, delete their child sizers automatically as well so in a typical situation you don't have to worry about freeing the sizers you create. Note, however, that if you Remove() a sizer from the window, it isn't automatically deleted any more and you are responsable for doing this.

How to create and use custom events?

Please look at the event wxWidgets sample source code, it shows how to do this among other things. Note that the way custom events are defined has changed in wxWidgets 2.3.1 as compared to the previous releases.

Why doesn't my code work when I create a window from a thread?

Using any GUI functions from the thread other than the main one (the one running the application event loop) is not supported, in particular creating windows from a worker thread will never work. If you need to do anything from the worker thread the simplest way to do it is to post a custom event to the main thread asking it to do whatever is necessary.

How can I set the TAB order of the controls?

Starting from wxWidgets 2.8 you can call wxWindow::MoveBeforeInTabOrder() and MoveAfterInTabOrder() to change the position of a child window in the TAB chain. Notice that by default the TAB order is the same as the order of creation.

What is the difference between _T(), wxT() and _()?

First of all, _T() is exactly the same as wxT() (it exists only because it should be more familiar to Windows programmers) which reduces the problem of choosing among the macros to use somewhat.

Here is some pseudo-code for choosing the macro to use between the remaining possibilities, that is whether to use wxT(), use _() or not use any of them:

	if ( string should be translated )
		use _("string")
	else if ( string should be in Unicode in Unicode build )
		use wxT("string")
		just use "string" normally

Note that if you don't care about Unicode at all, you don't have to use wxT() at all. On the contrary, if you do, note that _() takes care of it internally so if you use it your code will compile in both the ANSI and Unicode builds.

Please see the description of these macros in the manual for more details.

Why doesn't Esc close my dialog?

Pressing Esc will close the dialog if and only if it has a button with wxID_CANCEL id.

How can I get rid of message boxes with error messages?

These message boxes are probably due to calls to wxLogError() or other log functions from wxWidgets code. To completely suppress them you may use wxLogNull class, please see the manual for details. Do note, however, that a better solution is to avoid the error in the first place as suppressing these error message might hide other, important, ones.

How can I retrieve the path containing my executable?

This topic is covered in the technical note Writing installers.

Printf(str) works perfectly under Windows but crashes under Unix, why?

The following code:
wxString str;
str.Printf(wxT("My string is %s"), wxString("whatever"));
does not work. Unfortunately, it may seem to work fine under Windows because of a compiler quirk there but passing a wxString object to a function taking a variable number of arguments such as Printf() is undefined behaviour in C++. Accordingly, it will simply crash under most platforms but may even "work" on some of them.

You must use c_str() to make the above code work, i.e. write this instead:

wxString str;
str.Printf(wxT("My string is %s"), wxString("whatever").c_str());

Note that g++ should give you an error when passing an object to a vararg function like this -- another reason to compile your code with g++ even if you normally use another compiler.

XRC can't display non-ASCII characters correctly

If you use the wxXRC_USE_LOCALE flag (which is on by default), strings from XRC files are translated using wxLocale. wxLocale assumes the strings are in ASCII - if the are not, wxXmlResource leaves them in UTF-8 encoding in ANSI build of wxWidgets. Either don't use wxXRC_USE_LOCALE or use translate="0" attribute in XRC files. More details can be found here or here.


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